The present invention relates, in general terms, to clutches of the kind conventionally used for equipping motor vehicles.
As is known, such a clutch substantially comprises at least, axially in succession, a first plate, commonly called a reaction plate or flywheel, intended to be fixed in rotation to a first shaft, in practice a drive shaft such as the output shaft of the engine in the case of a motor vehicle, a friction disc intended to be fixed in rotation to a second shaft, in practice a driven shaft such as the input shaft of a gearbox in the case of a motor vehicle, a second plate, commonly called a pressure plate, fixed in rotation to the reaction plate, whilst being movable axially in relation to the latter, a component, called a cover, which is fixed by a fastening means to the reaction plate beyond the periphery of the pressure plate and the friction disc, and elastic means which, bearing on the cover, are designed to stress the pressure plate towards the reaction plate so as to clamp the friction disc axially between the said plates.
Apart from the fact that it makes it possible to attach the assembly to the shaft in question, in practice the reaction plate must perform several functions.
First of all, because of its mass it constitutes an inertial flywheel suitable for regulating the acyclic rotation of the shaft in question.
It must therefore have a mass sufficient for this purpose.
Furthermore, it is responsible for ensuring, at least to a certain extent, absorption and dissipation of the heat energy released as a result of friction when it comes in contact with the friction disc during engagement or disengagement of the clutch.
As above, it must have a mass sufficient for this purpose.
Moreover, since this is a clutch for a motor vehicle, it conventionally carries a starter ring.
It must therefore have a diametral extension sufficient to meet the requirements for installing the pinion intended to interact with this starter ring.
Likewise, when, as is also the case in some motor vehicles, the clutch is equipped with an ignition target, it must also have a diametral extension sufficient to meet the requirements for installing the sensor intended to interact with this ignition target.
The reaction plate is usually made in one piece, for example by moulding any material, such as cast iron or steel.
Because of the above-mentioned requirements of diametral extension, this component often has a substantial mass which is largely redundant as regards the sole parallel requirements of inertia and absorption of heat energy.
Such a component is therefore needlessly expensive and heavy.
Moreover, since its mass is redundant as regards the heat absorption requirement, it causes premature asymmetry in the heat exchanges which the friction disc undergoes, the pressure plate normally not having by itself a mass with an equivalent capacity for the absorption of heat energy.
The result of this can be, in particular, an unnecessary difference in the wear which the friction linings of this friction disc undergo on the respective faces.
To mitigate these disadvantages, in particular German Patent Application No. 2,853,298 has proposed making the reaction plate of an assembly of two separate parts, namely a transverse supporting bracket, by means of which the said reaction plate assembly can be fixed to the shaft in question, and a reaction element with which the friction disc can interact.
It would thus be possible to match both of these parts as closely as possible to the functions which they have to perform, and this would make it possible, in particular, in a substantially cheaper and lighter assembly, to assist in ensuring a symmetry of the heat exchanges which the friction disc undergoes on the respective faces.
However, in German Patent Application No. 2,853,298, the fastening means fixing the two parts forming the reaction plate assembly to one another are separate from those fixing the cover to this reaction plate assembly.
This results in a multiplicity of fastening means to be used, which is detrimental to the sought-after saving and lighter weight.
Furthermore, in German Patent Application No. 2,853,298, the cover is fastened to the supporting bracket of the reaction plate assembly, and, since it therefore extends annularly beyond the reaction element it necessarily has a considerable size in the axial and diametrial directions, again detrimental to the sought-after saving and lighter weight.
Finally, although in this German Patent Application No. 2,853,298 the reaction element bears on the supporting bracket, with which it is associated, only by means of local seats which form recesses circumferentially between them, most of these are masked by the cover which bears circumferentially by means of a radial edge on the said supporting bracket, with the exception of some notches of limited extension made in the said edge and the corresponding side wall, and which are provided to allow free play to the fastening means fixing the reaction element to the said supporting bracket and to attach the reaction element to the said cover.
The result of this is that the internal space contained between the supporting bracket and the reaction element, and consequently the corresponding face of the latter, are not ventilated in a satisfactory manner.
The same is true in French Pat. No. 1,110,406, in which the fastening means fixing the reaction plate assembly to the cover also fix the two parts forming the reaction plate assembly to one another, with one of these parts bearing circularly on the other.
The subject of the present invention is, in general terms, an arrangement which, avoiding these disadvantages, makes it possible to gain more benefit from making the reaction plate assembly in two separate parts, in particular ensuring good ventilation of its internal space.